All depends on your definition of these words.
For me zerging is when your soldiers' life expectancy is 1-3 missions, normal play is when it is 4-25, life expectancy of 25+ missions goes against the game design (in my opinion).
If (for you) life expectancy below 25-30 missions is zerging, and soldiers only become "useful" after that... you play a completely different game, not xcom.
Btw. "every soldier can reach his statscaps in ~25-30 missions" is true only if you abuse various active training procedures... which is absolutely lame. I have a few of such soldiers (even in my current LP) and they are nowhere near reaching all stats caps, not even close. Attached is an example with my best soldier, which survived from the very beginning (Jan 1999, day 1) until now (end of January 2000, almost end game).
The only stats which i put into active training with ambushes is reactions, because i consider it a vital one in the survival of the soldiers. Everything else maxes out over time, as long as they survive.
It also depends greatly on how you play.
I seldomly enter buildings at all, i blow them into pieces then the tank takes a look and everything which dares to survive the use of explosives gets blasted by my Soldiers.
It's a simple tactic and you my think it is a cheap tactic, but it increases your survival rate to a big degree.
Also you do not need to enter most UFO's at all, you can just blast the aliens as they step outside, of course this won't work against some aliens like Ethereals. So it depends.
And killing Mutons with Laser Pistol / Plasma Pistol reactionfire is a pretty decent way to improve your reactions.
And yes this might seem as abuse of the 20 turn aliens move out thing, but they also leave the UFO before turn 20 and when after a couple of turns no else steps out, then i step in and kill them, because i do not want to wait until turn 30+, to end my mission.
If you do a mission right noone dies, you also can improve your survival rate combining strafing and mutual surprise (to safely peak around corners), and set up ambushes yourself.
It also has todo with using the terrain in which you operate to your advantage and think before you move. Never scout with your last soldier, for example, place Proxy grenades on cave entrences and so forth. Or simply blow away half a hill to kill the alien inside the cave.
If your ingame creativity stops at entering buildings, or entering caves, which basically incline a soldier death within a short amount of time, then i can only say you are a poor commander, sorry. I play the game to win, to let my Soldiers survive and if they die, because i was to stupid and did something wrong ok then they are dead, next rookie is waiting to get trained anyway.
If i spot a alien i make sure it dies in the same turn, doesn't always work out that way, but you have various other options, like throwing smoke and obscuring his LOS, or simply pray for a random damage modifier which doesn't give you a instant death.
And the name of my Mod is Hardmode Expansion, not "Hardmode", and it is my first expansion mod i am writing and my first serious introduction to modding, so it is expected that not everything works out the way i wanted it to be, but that is not a big deal, since i can learn and adept.
And if you do not like my Mod ok, so do not play it.
